Exploring, drilling and completing hydrocarbon and other wells are generally complicated, time consuming and ultimately very expensive endeavors. As a result, oilfield efforts are often largely focused on techniques for maximizing recovery from each and every well. Whether the focus is on drilling, unique architecture, or step by step interventions the techniques have become quite developed over the years. In large scale oilfield operations, the development of the well and follow-on interventions may be carried out through the use of several positive displacement pumps. For example, in applications of cementing, coiled tubing, water jet cutting, or hydraulic fracturing of underground rock, 10 to 20 or more pumps may be simultaneously utilized at the oilfield for a given application.
Each positive displacement pump may be a fairly massive piece of equipment with associated engine, transmission, crankshaft and other parts, operating at between about 200 Hp and about 4,000 Hp. A large plunger is driven by the crankshaft toward and away from a chamber in the pump to dramatically effect a high or low pressure. This makes it a good choice for high pressure applications. A positive displacement pump is generally used in applications where fluid pressure exceeding a few thousand pounds per square inch gauge (psig) is required. Hydraulic fracturing of underground rock, for example, often takes place at pressures ranging from a few hundred to over 20,000 psig to direct an abrasive containing slurry through an underground well to release oil and gas from rock pores for extraction. A system with 10-20 pumps at the oilfield may provide a sufficient flowrate of the slurry for the application, for example, between about 60-100 barrels per minute (BPM).
In the above described multi-pump system, each one of the pumps are fluidly connected to a manifold which delivers the slurry fluid to the wellhead. Thus, the pumps are hydraulically linked to one another. As a result, while each pump may be subject to its own individual wear and performance factors, the efficiency and health of the overall system is subject to factors such as fluctuating pressure and flow interaction among all of the pumps.
One circumstance where the health of the overall system may be of concern due to multi-pump interaction is in the case of excessive, prolonged, or cumulative vibrations reverberating through the lines. For example, with a variety of pumps utilized, it is unlikely that all of the pumps will continuously pump in sync with one another. Nevertheless, from time to time, multiple pumps of the system may randomly come into phase or sync with one another as they pump. When this occurs, the inherent vibrations from pumping are cumulatively felt by the system, often in dramatic fashion.
More specifically, for any given pump, the plunger reciprocates in a sinusoidal fashion as described above. That is, while a mean flow may be obtained from each pump, the reality is that at any given moment, the pump flow rate follows a sinusoidal curve in terms of position over time. Thus, the above described vibration is seen at each pump during operation. Once more, when the vibration from several pumps come into harmony with one another, the degree of vibration may damage the system. By way of specific example, this damage may include harm to valves, the manifold or the rupturing of an exposed line often at an elbow or at some other natural weakpoint.
Rupturing of a line in particular may be catastrophic to operations. For example, recalling that the extremely high flow rate and pressures involved, this may present itself as an explosion-like event at the oilfield. Thus, operator safety may be of greatest concern. Once more, in addition to repair and/or replacement cost of the ruptured line, there is a high probability that other adjacent high dollar equipment would also be subject to damage and also require repair and/or replacement. Further, regardless the extent of the damage, there will be a need to shut down all operations at the wellsite for damage assessment and remediation of the system before operations may resume. Ultimately, even in fortunate circumstances where operator injury is avoided, there will still be potentially hundreds of thousands of dollars of capital and time lost due the vibration-induced system damage.
In an effort to avoid vibration-induced system damage as a result of multiple pumps coming into sync with one another, efforts may be undertaken to ensure that all pumps are kept out of sync with each other. Specifically, in theory, each pump may be extensively monitored and controlled to help avoid synchronization or constructive interference at various locations along the manifold. For example, sensors at each pump may be employed along with real-time controls for continuously monitoring and adjusting the phase of each pump to ensure that multiple pumps are never allowed to come into sync with one another, as manifested by measuring the peak-to-peak pressure pulsation or vibration amplitude at various locations along the manifold.
Unfortunately, simultaneously monitoring and controlling 10 to 20 pumps at the oilfield in this manner is not generally a practical endeavor. That is, as noted above, each pump is a massive piece of equipment reciprocating at a very high rate of speed. Thus, the ability to not only manually precisely adjust the timing of each pump in real-time, but to also do so on the fly based on the phase of each and every other pump quickly becomes a largely impractical endeavor. Therefore, as a practical matter, operators are generally left manually monitoring piping and pumps for unduly high vibrations and taking control action, such as manually adjusting pump rates. However, given the manual nature of this particular undertaking, the avoidance of sudden catastrophic vibration damage is hardly assured.